Plastic blow molding is conventionally performed by providing a hot plastic parison either from extruded plastic or as a preform which is usually injection molded from plastic. Usually, such preforms are composed of a single type of plastic that is injected into a mold through a single port. However, there have also been attempts to provide coinjection of more than one plastic into a mold so as to provide different layers of plastic.
U.S. Pat. No. 3,878,282 to Bonis et al. discloses a process for molding multi-layer articles that are specifically disposed as a preform-type parison with different layers. The process involved is performed by injection molding the different layers within different molds while mounted on the same inner mandrel during the injection of each layer.
U.S. Pat. No. 4,307,137 to Ota et al. discloses a method for forming an optical design pattern in polyethylene terephthalate articles which are specifically disclosed as a blow molding preform having inner and outer members with the inner member having an open end defining a thread closure and with the outer member having a junction with the inner member toward a closed end of the preform from the thread closure.
U.S. Pat. No. 4,391,861 to Nilsson discloses a preform of a thermoplastic and has a two-part interfitted construction and at least one intermediate layer that functions as a gas barrier, and also discloses that the outer part may be previously used and reprocessed material.
U.S. Pat. No. 4,646,925 to Nohara discloses a multi-layer preform for draw-blow forming a bottle which has inner and outer layers with a junction that is located toward a closed end of the preform from a closure thread at an open end of the preform. The preform also includes a gas barrier intermediate the inner and outer layers.
U.S. Pat. No. 5,102,705 discloses a bottle made of polyethylene naphthalate resin produced by highly stretching a preform in a manner that is disclosed as limiting gas permeability and x-ray transmission.
There have been attempts in the past, such as disclosed by the aforementioned Nilsson patent, to utilize post consumer recycled plastic for plastic blow molding since such reuse reduces the need for additional land fills as well as conserving on natural resources in the manufacturing of new articles. Such prior attempts have utilized injection molding or extrusion which necessarily limits the amount of post consumer recycled plastic which can be utilized since it is difficult to injection mold or extrude relatively thin wall preforms used for plastic blow molding. The maximum amount of post consumer recycled plastic which has been used to date is about 50% by weight of the total weight of the preform.
Blow molding has also previously been performed utilizing a preform that is initially thermoformed from film, i.e. sheet plastic, that provides a moisture and/or oxygen barrier prior to injection molding of an outer protective layer. After the thermoforming, the formed film is trimmed and the outer layer is then injection molded around the thermoformed plastic prior to the finished preform being blow molded to provide the resultant container.
The dominant gas barrier commercially utilized at the present time to prevent gas transmission through blow molded containers is ethyl vinyl alcohol which may be dipped, sprayed or brushed as well as coinjected with plastic resin. One disadvantage of ethyl vinyl alcohol is that it must be fully enveloped by the plastic of the preform or it will tend to draw moisture from the atmosphere and thereby loses its ability to function in preventing gas transmission through the container.